Synthesis of hydrophobic trimethoxybenzene-formaldehyde gels - controlling the microstructure

Abstract

Aerogels based on phenolics (such as resorcinol-formaldehyde, RF) are receiving increasing attention due to their remarkable thermal insulating and lightweight properties that can be traced back to their unique microstructure (including high open porosity and low density).[1] While structure and, thus, properties of these organic aerogels are typically tuned by controlling parameters such as the monomer concentrations, temperature, type of catalyst and pH-value, the influence of the solvent on gelation is only scarcely exploited.[2] Especially, the pH-value is important to tune the microstructures and, therefore, also the surface characteristics of RF by modifying the relative kinetics of addition and condensation reactions during gelation.[3] We recently developed trimethoxybenzene-formaldehyde (TMBF) aerogels as hydrophobic analog of RF.[4] Here, we report on their synthesis and characterization by chromatographic (HPLC), scattering (DLS), spectroscopic (ATR-IR, NMR) methods as well as pycnometry, sorption analysis and electron microscopy. The influence of the nature of the solvent on the microstructure of the resulting gels is demonstrated. While resembling RF aerogels in many ways, TMBF aerogels show remarkably different wetting behavior. [1] X. Lu, M. C. Arduini-Schuster, J. Kuhn, O. Nilsson, J. Fricke, R. W. Pekala, Science 1992, 255, 971-972. [2] A. M. ElKhatat, S. A. Al-Muhtaseb, Adv. Mater. 2011, 23, 2887-2903. [3] K. Barral, J. Non-Cryst. Solids 1998, 225, 46-50. [4] T. Anklam, C. Farès, R. Tannert, in 7th International Conference on Multifunctional, Hybrid and Nanomaterials (Eds.: M. Antonietti, C. Sanchez, R. Xu), Elsevier, Genova, Italy, 2022.